Powdered and aqueous salt solutions find many applications in the transportation industry. Powdered salts such as sodium chloride and magnesium chloride, as well as aqueous brines of these salts, can be applied to roads, bridges, and other transport surfaces to suppress the formation and accumulation of snow and ice. Aqueous salt brines are also used for dust control on paved and unpaved roads, especially where dry and windy weather conditions are prevalent. These solutions may also be applied to exposed surfaces of loads of dirt, gravel, coal, and other dust producing materials as they are being transported.
Unfortunately, halide salts can cause severe corrosion in many materials, including the metals used in vehicles and reinforced concrete. This corrosion not only increases the costs of vehicle maintenance and repair, but also creates safety hazards such as deteriorating concrete, broken bolts and fasteners, and rusting rail lines. The cumulative impact of these problems has caused many states to limit the use of salt on roads.
One alternative has been to sand, gravel, and other abrasives instead of halide salts to reduce effects of snow and ice on roads. While these materials may not substantially lower the freezing temperature of water like halide salts, they can increase the coefficient of friction between the road and vehicle tires. However, sand and gravel can also cause significant property damage when particulates are kicked up by fast moving vehicles. Dents in vehicle paneling and cracks in vehicle windshields are common occurrences when sand and gravel have been applied on a highway or other high-speed road. The use of sand and abrasives has also been proven to contribute to air and waterway pollution.
Another alternative has been to add corrosion inhibitors to halide brines in order to reduce the corrosive effects of the halide salts. These corrosion inhibitors have included chromates, phosphates, zinc salts, and nitrites. Unfortunately, all of these corrosion inhibitors have side effects that make them less than ideal for transportation applications. For example, while the nitrites may reduce the corrosive effects of halide salts across large surface areas, they may actually increase the rate of localized spot corrosion, rapidly increasing perforation in metals. Corrosion inhibitors that use salts of transition metals like chromium and zinc have raised environmental concerns due to their potential toxicity. Phosphates also raise environmental concerns due, among other reasons, to their unpredictable effects on plant and algae growth. Thus, there is a need for new anticorrosion agents that can be mixed with halide salts to significantly reduce the corrosive effects of those salts. This and other problems are addressed below.